Directional coupler based on a profiled microstrip coupling patch

Abstract

The application provides a directional coupler based on a special-shaped microstrip coupling sheet, which comprises a circular main rod, a rectangular coupling hole and a microstrip circuit board; the circular main rod serves as an outer conductor of a coaxial transmission line, and its two ends are an input through end and an output through end, and a rectangular coupling hole is formed in the outer wall; the microstrip circuit board is arranged outside the circular main rod and keeps a fixed distance from the circular main rod, and comprises a dielectric substrate, a special-shaped microstrip coupling sheet, a coupling end microstrip line, an isolation end microstrip line and a metallized via; the special-shaped microstrip coupling sheet is formed by coiling a microstrip line, is printed on one side of the dielectric substrate facing the circular main rod, and is electromagnetically coupled with the circular main rod through the rectangular coupling hole; the coupling end microstrip line and the isolation end microstrip line are printed on the other side of the dielectric substrate and are connected with two ends of the special-shaped microstrip coupling sheet through the metallized via. In this way, the application can significantly improve the return loss and the directivity index under the condition of limited space and fixed distance, and has a simple structure and is easy to implement.

Description

Technical Field

[0001] This invention relates to the field of microwave passive device technology, specifically to a directional coupler based on an irregularly shaped microstrip coupler, which is particularly suitable for signal coupling and power monitoring applications in cavity filter circuit boards in the radio frequency field. Background Technology

[0002] In radio frequency communication systems, directional couplers are widely used for critical functions such as power monitoring, signal distribution, and transmit / receive isolation. Traditional microstrip couplers mostly employ a parallel linear coupling line structure, and their performance is limited by the difference in odd and even mode phase velocities caused by the non-uniformity of the dielectric substrate, which in turn affects the directivity performance.

[0003] Furthermore, when such couplers are integrated into RF cavity filters, the relative height between the circuit board and the main frame is usually strictly limited due to mechanical assembly space constraints, making it impossible to optimize coupling efficiency by adjusting the spacing. In this case, parameter adjustments can only be made based on the microstrip pattern shape and coupling aperture size, resulting in extremely limited design freedom. Conventional rectangular microstrip structures are prone to port mismatch and directivity degradation under these constraints, and are sensitive to manufacturing errors, leading to poor batch consistency.

[0004] Therefore, there is an urgent need for a technical solution that can effectively improve return loss and directivity under fixed spatial conditions. Summary of the Invention

[0005] The purpose of this invention is to provide a directional coupler based on an irregularly shaped microstrip coupler to solve the technical problems of high return loss and insufficient directivity caused by traditional rectangular microstrip couplers under the constraint of fixed relative height between the microstrip circuit board and the circular main rod.

[0006] To achieve the above-mentioned technical effects, the present invention provides a directional coupler based on an irregularly shaped microstrip coupling plate, applied to a cavity filter circuit board, comprising:

[0007] The circular main rod serves as the outer conductor of the coaxial transmission line, with its two ends forming an input through-hole and an output through-hole, respectively, and a rectangular coupling hole is provided on its outer wall.

[0008] A microstrip circuit board is disposed on the outside of the circular main rod, and the distance between the microstrip circuit board and the circular main rod is set to a fixed relative height.

[0009] The microstrip circuit board includes a dielectric substrate, a shaped microstrip coupling sheet, a coupling end microstrip line, an isolation end microstrip line, and metallized vias.

[0010] The irregularly shaped microstrip coupling sheet is formed by winding microstrip lines, and the corners of the microstrip lines that make up the irregularly shaped microstrip coupling sheet are rounded. The irregularly shaped microstrip coupling sheet is printed on the surface of the dielectric substrate facing the circular main rod, and is disposed opposite to the rectangular coupling hole, so as to perform electromagnetic energy coupling with the circular main rod through the rectangular coupling hole.

[0011] The coupling end microstrip line and the isolation end microstrip line are printed on the surface of the dielectric substrate facing away from the circular main rod; the two ends of the irregularly shaped microstrip coupling piece are respectively connected to the coupling end microstrip line and the isolation end microstrip line through the metallized vias.

[0012] Furthermore, the irregularly shaped microstrip coupling piece is located directly above the circular main rod, and the main coupling area of ​​the irregularly shaped microstrip coupling piece is located within the rectangular coupling hole.

[0013] Furthermore, the dielectric substrate is made of FR4 material with a dielectric constant of 4.4 and a dielectric thickness of 0.8 mm.

[0014] Furthermore, a metallized via is provided on each side of the irregularly shaped microstrip coupling piece, and the two ends of the irregularly shaped microstrip coupling piece are respectively connected to the coupling end microstrip line and the isolation end microstrip line through the two metallized vias.

[0015] Furthermore, the overall size of the irregularly shaped microstrip coupling sheet is 14mm × 4.5mm; the width of the microstrip lines constituting the irregularly shaped microstrip coupling sheet is 1mm, and the spacing between the lines is 0.63mm.

[0016] Furthermore, the width of the coupling end microstrip line is 1.4 mm; the width and length of the isolation end microstrip line are 0.7 mm and 4 mm, respectively, and a standard 50 Ω port is formed by RLC lumped ground.

[0017] Furthermore, the rectangular coupling hole has chamfers around its perimeter; the length and width of the rectangular coupling hole are 16mm and 8.5mm respectively, and the chamfers around its perimeter are 2mm.

[0018] The directional coupler based on irregularly shaped microstrip couplers provided by this invention only requires adjusting the planar geometry of the microstrip coupler without adding any additional components. It has a simple structure, is easy to manufacture, and is inexpensive. It is particularly suitable for space-constrained applications in cavity filter circuit boards where the distance between the microstrip circuit board and the main rod is fixed and the size of the circular main rod is fixed. It solves the technical problems of port mismatch and directionality degradation of traditional rectangular microstrip couplers under such constraints. Attached Figure Description

[0019] Figure 1This is a perspective view of the overall structure of the directional coupler based on the irregularly shaped microstrip coupling sheet provided in an embodiment of the present invention;

[0020] Figure 2 A perspective view of the planar structure of an existing conventional rectangular microstrip coupling sheet;

[0021] Figure 3 This is a schematic diagram of the simulation results of the directional coupler based on the irregular microstrip coupling sheet provided in an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of the structure of the irregularly shaped microstrip coupling plate in the directional coupler based on the irregularly shaped microstrip coupling plate provided in an embodiment of the present invention;

[0023] The attached diagram is labeled as follows: 1. Input through-hole; 2. Output through-hole; 3. Coupled end; 4. Isolation end; 10. Irregular microstrip coupling plate. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] It should be noted that references to "an embodiment," "embodiment," "example embodiment," etc., in this specification refer to the described embodiment including specific features, structures, or characteristics, but not every embodiment must include these specific features, structures, or characteristics. Furthermore, such expressions do not refer to the same embodiment. Moreover, when describing specific features, structures, or characteristics in conjunction with embodiments, whether or not explicitly described, it is indicated that incorporating such features, structures, or characteristics into other embodiments is within the knowledge of those skilled in the art.

[0026] Figure 1 This invention illustrates a directional coupler based on an irregularly shaped microstrip coupling plate, which is applied to a cavity filter circuit board and includes a circular main rod and a microstrip circuit board.

[0027] The circular main rod serves as the outer conductor of the coaxial transmission line, with its two ends forming an input through-hole 1 and an output through-hole 2, respectively, and a rectangular coupling hole is provided on its outer wall.

[0028] The microstrip circuit board is disposed on the outside of the circular main rod, and the distance between the microstrip circuit board and the circular main rod is set to a fixed relative height; the fixed relative height means that the distance between the microstrip circuit board and the circular main rod is a fixed value.

[0029] The microstrip circuit board includes a dielectric substrate, a shaped microstrip coupling piece 10, coupling end microstrip lines, isolation end microstrip lines, and metallized vias. The shaped microstrip coupling piece 10 is formed by winding microstrip lines, and the corners of the microstrip lines forming the shaped microstrip coupling piece are rounded. The shaped microstrip coupling piece is printed on the surface of the dielectric substrate facing the circular main rod and is positioned opposite to the rectangular coupling hole for electromagnetic energy coupling with the circular main rod through the rectangular coupling hole. That is, the shaped microstrip coupling piece 10 is a coupling piece with a non-rectangular planar geometry compared to a traditional rectangular microstrip coupling piece. The rounded corner transition refers to the use of an arc-shaped transition at the corner of the microstrip line to reduce discontinuities.

[0030] The coupling end microstrip line and the isolation end microstrip line are printed on the surface of the dielectric substrate facing away from the circular main rod. The two ends of the irregularly shaped microstrip coupling piece 10 are connected to the coupling end microstrip line and the isolation end microstrip line respectively through the metallized vias. Specifically, the end of the coupling end microstrip line forms a coupling end 3, and the end of the isolation end microstrip line forms an isolation end 4. The coupling end 3 is used to output the signal coupled from the circular main rod, and the isolation end 4 is used to connect a matching load or lumped ground to improve the directivity of the directional coupler.

[0031] Specifically, the irregularly shaped microstrip coupling piece 10 is located directly above the circular main rod, and the main coupling area of ​​the irregularly shaped microstrip coupling piece 10 is located within the range of the rectangular coupling hole; the main coupling area refers to the main area of ​​the irregularly shaped microstrip coupling piece 10 that is directly opposite the rectangular coupling hole and actually participates in electromagnetic energy coupling.

[0032] In this embodiment, the dielectric substrate is preferably an FR4 substrate with a dielectric constant of 4.4 and a dielectric thickness of 0.8 mm.

[0033] Furthermore, a metallized via is provided on each side of the irregular microstrip coupling piece 10, and the two ends of the irregular microstrip coupling piece 10 are respectively connected to the coupling end microstrip line and the isolation end microstrip line through two metallized vias; wherein, the metallized via refers to a conductive through hole that penetrates the dielectric substrate and realizes the electrical connection of different layers of metal patterns.

[0034] The overall dimensions of the irregularly shaped microstrip coupling sheet 10 in this embodiment are 14mm × 4.5mm; the width of the microstrip lines constituting the irregularly shaped microstrip coupling sheet 10 is 1mm, and the spacing between the lines is 0.63mm.

[0035] In this embodiment, the circular main rod serves as the outer conductor of the coaxial transmission line, with air filling between its inner and outer conductors. A rectangular coupling hole is formed on the outer wall of the circular main rod. This rectangular coupling hole is used to achieve electromagnetic energy coupling between the coaxial main transmission line and the microstrip coupling structure. The microstrip circuit board is disposed outside the circular main rod, and its fixed relative height to the circular main rod is determined by the overall structural layout and is a non-adjustable design constraint parameter.

[0036] like Figure 2 As shown, conventional rectangular microstrip couplers employ a parallel straight-line coupling line structure. Their performance is limited by the difference in odd and even mode phase velocities caused by the non-uniformity of the dielectric substrate, and they are prone to port mismatch and directivity degradation under space-constrained conditions. This embodiment improves upon these problems by modifying the rectangular microstrip coupler into an irregularly shaped microstrip coupler 10.

[0037] like Figure 4 As shown, the irregularly shaped microstrip coupling piece 10 is formed by coiling microstrip lines and occupies a rectangular space. The corners of the microstrip lines constituting the irregularly shaped microstrip coupling piece 10 are rounded, with a preferred radius of 0.25±0.1mm to reduce signal reflection. The two ends of the irregularly shaped microstrip coupling piece 10 are connected to the coupling end microstrip line and the isolation end microstrip line respectively through metallized vias, with a preferred diameter of 0.3±0.1mm. The main coupling area of ​​the irregularly shaped microstrip coupling piece 10 is located within the rectangular coupling hole, allowing the irregularly shaped microstrip coupling piece 10 to couple signals with the circular main rod without obstruction through the rectangular coupling hole.

[0038] In this embodiment, the operating frequency band is set to 0.7~1.0GHz, and the center frequency is... f 0 = 850MHz. The outer conductor diameter of the circular main rod is 10mm, and the inner conductor diameter is 4.3mm. The length and width of the rectangular coupling hole are 16mm and 8.5mm, respectively, with a 2mm chamfer on all four sides. The overall size of the irregular microstrip coupling piece 10 is 14mm × 4.5mm, the width of the microstrip lines constituting the irregular microstrip coupling piece 10 is 1mm, and the spacing between the lines is 0.63mm. The thickness of the microstrip lines on the surface and bottom layers of the circuit board is 0.035mm. The width of the microstrip line at the coupling end is 1.4mm; the width and length of the microstrip line at the isolation end are 0.7mm and 4mm, respectively, and a standard 50Ω port is formed by RLC lumped ground. The above parameters were optimized and adjusted through simulation. The adjustment objects include the microstrip line width constituting the irregular microstrip coupling piece 10, the spacing between the coiled microstrip lines, the overall size of the irregular microstrip coupling piece 10, and the size of the rectangular coupling hole, etc.

[0039] like Figure 3As shown in the diagram (S31 represents coupling, S32 represents isolation, and S33 represents return loss), simulations reveal that within the 0.7–1.0 GHz frequency band, the weakest coupling is 37.68 dB, the worst return loss is 31.1 dB, and the worst isolation is 76.5 dB, indicating that return loss and isolation (isolation - coupling = directivity) have significant margins. Compared to traditional rectangular microstrip couplers, this invention optimizes return loss and directivity margins by 5–10 dB or more while maintaining relatively stable coupling strength.

[0040] Furthermore, the width of the coupling end microstrip line is 1.4 mm; the width and length of the isolation end microstrip line are 0.7 mm and 4 mm, respectively, and a standard 50 Ω port is formed by RLC lumped ground.

[0041] The rectangular coupling hole has chamfers around its perimeter; the length and width of the rectangular coupling hole are 16mm and 8.5mm respectively, and the chamfers around its perimeter are 2mm.

[0042] In summary, the directional coupler based on irregularly shaped microstrip coupling plates provided by this invention only requires modification of the planar geometry of the microstrip coupling plate, without the need for additional components. It has a simple structure and is easy to implement. It is particularly suitable for space-constrained application scenarios in cavity filter circuit boards where the distance between the microstrip circuit board and the main rod is fixed and the size of the circular main rod is fixed. It solves the technical problems of port mismatch and directionality degradation of traditional rectangular microstrip coupling plates under such constraints.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0044] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A directional coupler based on an irregularly shaped microstrip coupling plate, applied to a cavity filter circuit board, characterized in that, Including: The circular main rod serves as the outer conductor of the coaxial transmission line, with its two ends forming an input through-hole and an output through-hole, respectively, and a rectangular coupling hole is provided on its outer wall. A microstrip circuit board is disposed on the outside of the circular main rod, and the distance between the microstrip circuit board and the circular main rod is set to a fixed relative height. The microstrip circuit board includes a dielectric substrate, a shaped microstrip coupling sheet, a coupling end microstrip line, an isolation end microstrip line, and metallized vias. The irregularly shaped microstrip coupling sheet is formed by winding microstrip lines, and the corners of the microstrip lines that make up the irregularly shaped microstrip coupling sheet are rounded. The irregularly shaped microstrip coupling sheet is printed on the surface of the dielectric substrate facing the circular main rod, and is disposed opposite to the rectangular coupling hole, so as to perform electromagnetic energy coupling with the circular main rod through the rectangular coupling hole. The coupling end microstrip line and the isolation end microstrip line are printed on the surface of the dielectric substrate facing away from the circular main rod; the two ends of the irregularly shaped microstrip coupling piece are respectively connected to the coupling end microstrip line and the isolation end microstrip line through the metallized vias.

2. The directional coupler based on an irregularly shaped microstrip coupling plate according to claim 1, characterized in that, The irregularly shaped microstrip coupling piece is located directly above the circular main rod, and the main coupling area of ​​the irregularly shaped microstrip coupling piece is located within the rectangular coupling hole.

3. The directional coupler based on an irregularly shaped microstrip coupling plate according to claim 1, characterized in that, The dielectric substrate is made of FR4 material with a dielectric constant of 4.4 and a dielectric thickness of 0.8 mm.

4. The directional coupler based on an irregularly shaped microstrip coupling plate according to claim 1, characterized in that, The irregularly shaped microstrip coupling plate has a metallized via on each side, and the two ends of the irregularly shaped microstrip coupling plate are respectively connected to the coupling end microstrip line and the isolation end microstrip line through the two metallized vias.

5. The directional coupler based on an irregularly shaped microstrip coupling plate according to claim 1, characterized in that, The overall dimensions of the irregularly shaped microstrip coupling sheet are 14mm × 4.5mm; the width of the microstrip lines that make up the irregularly shaped microstrip coupling sheet is 1mm, and the spacing between the lines is 0.63mm.

6. The directional coupler based on an irregularly shaped microstrip coupling plate according to claim 1, characterized in that, The width of the coupling end microstrip line is 1.4 mm; the width and length of the isolation end microstrip line are 0.7 mm and 4 mm, respectively, and a standard 50Ω port is formed by RLC lumped ground.

7. The directional coupler based on an irregularly shaped microstrip coupling plate according to claim 1, characterized in that, The rectangular coupling hole has chamfers around its perimeter; the length and width of the rectangular coupling hole are 16mm and 8.5mm respectively, and the chamfers around its perimeter are 2mm.

Images